Significant advances have been made in recent years with respect to using heterogeneous catalysts for converting biomass-derived compounds to fuels and chemicals. Conventional approaches deconstruct solid cellulose into smaller molecules that are soluble in various solvents (e.g., water, ionic liquids), thereby allowing transport of these reactants to the active sites on the heterogeneous catalyst, the majority of which are located within the pores of a high-surface area material. A difficulty in implementing this strategy is that chemical components used to deconstruct solid cellulose (e.g., sulfuric acid) may alter the performance of heterogeneous catalysts used subsequently to convert the soluble biomass-derived reactants to the desired fuels and/or chemicals. As a result, costly purification steps are required to implement a cascade catalytic process. Thus, the present method addresses a long-felt and unmet need by providing a route to levulinic acid and gamma-valerolactone that uses gamma-valerolactone itself as an extraction solvent to extract levulinic acid from an aqueous solution.
In short, there is an increasing need for methods to produce fuels and chemicals from renewable, domestic sources to reduce the dependence on the fossil sources of carbon. A great many processes have been reported in the literature; however, scale-up of these processes to industrial scale has been severely hampered due to the necessity of purifying the final products and/or intermediates. Purification is often required to avoid negatively impacting downstream catalytic processes. Levulinic acid, for example, is a building block that can be upgraded to value-added chemicals and liquid transportation fuels by several pathways. Levulinic acid, however, is conventionally produced by cellulose deconstruction using dilute solutions of mineral acids. The mineral acid needs to be removed prior to downstream processes, such as hydrogenation to gamma-valerolactone (GVL). If the acid is not removed, the downstream reactions are severely impacted or rendered infeasible.
In co-pending and co-owned application Ser. No. 13/115,420 is described a strategy that uses alkylphenols as a solvent for a biphasic extraction. Alkylphenols are insoluble in water, and thus separate from aqueous solutions of the cellulose deconstruction feed, while also extracting a portion of the levulinic acid. Even though alkylphenol extraction has significant advantages over previous processes, there are still some drawbacks. It uses an external solvent, requires final purification of the product by distillation, and has a moderate partition coefficient: approximately 2 for levulinic acid (concentration of levulinic acid in the organic phase divided by the concentration of levulinic acid in the aqueous phase). Also, the partition coefficient for formic acid (a co-product in the production of levulinic acid from cellulose) is less than 0.2. Thus, in the earlier process, formic acid cannot be used as internal source of H2.